Semiconductor devices are used in a variety of electronic applications, such as, for example, personal computers, cell phones, digital cameras, and other electronic equipment. The semiconductor industry continues to improve the integration density of various electronic components (e.g., transistors, diodes, resistors, capacitors, etc.) by continual reductions in minimum feature size, which allow more components to be integrated into a given area. In some devices, multiple dies are stacked vertically to reduce the footprint of a device package and permit dies with different processing technologies to be interconnected.
Devices may be stacked and interconnected by bonding dies directly to each other. In some cases, dies are bonded in bulk by bonding wafers having multiple dies on each wafer. Components on different wafers or different are interconnected with metal lines that are exposed at the bonding surface of the dies and brought into contact during bonding. After bonding, the metal lines provide electrical connectivity between the dies.